2.9 ALKENES EXTRA QUESTIONS MS. (b) Addition 1 (ignore self or chain as a preface to addition ) (penalise additional)

Transcription

1 2.9 ALKENES EXTRA QUESTIONS MS 1. (a) (b) Addition 1 (ignore self or chain as a preface to addition ) (penalise additional) 2. Electrophilic addition 1 M1: curly arrow from = bond towards/alongside the side of atom on 1 OSO 2 O 1 (penalise M1 if arrow to 2 SO 4 OR to formal charge on of 1 O bond) (ignore partial charges on and O of 2 SO 4, but penalise if these are incorrect on the atom being attacked) (credit M1 and M2 if correct curly arrow to provided the anion is present) M2: curly arrow from O bond towards/alongside the side of the O atom on OSO 2 O 1 (credit the arrow even if there are partial or formal charges on and O but the structure of 2 SO 4 is correct) M: correct structure of the carbocation 1 (penalise use of sticks in this structure) M4: curly arrow from lone pair on an individual oxygen atom of (correct formula for) hydrogensulphate ion towards/alongside atom bearing the positive charge 1 (insist that the an ion has the correct formula with a lone pair of electrons and a negative charge). Type of isomerism geometrical or E-Z Explanation restricted rotation or double bond rigid 2 4. [2] [5] [2] accept and redit 1 mark for a correct formula for but-2-ene redit 1 mark for any pair of cis / trans isomers Geometric(al) Or cis-trans Or diastereoisomerism NOT stereoisomerism [] Mill ill igh School 1

2 5. (i) 2 or (ii) Reagent(s) Br 2 or KMnO 4 Observation(s) no charge 6. (i) Electron pair/ lone pair acceptor OR seeking/bonds with an electron pair 1 (insist on reference to a pair of electrons) [] (ii) M1 curly arrow from middle of = bond of the alkene towards/ alongside the atom of the -Br; 1 (penalise arrows which go towards one of the carbon atoms) (ignore a partial negative charge on the =) M2 curly arrow from -Br bond to side of Br atom; 1 (penalise M2 if there are formal charges on Br or if there are partial charges which are the wrong) (penalise M2 if the single bond has two dots in addition to the line) M correct structure for carbocation; 1 (penalise M if the positive charge is placed on the end of a bond) (penalise M if any alkene other than ethene is used - all other marks can score) M4 curly arrow from lone pair on bromide ion to the positive carbon 1 of carbocation, ensuring that bromide ion has a negative charge; [5] 7. (a) Ml credit a correct structure for either geometrical isomer and its 1 designation as either cis or trans. OR credit two correct geometrical isomer structures (ignore the names) OR credit two correct names for cis pent-2-ene and trans pent-2-ene (ignore the structures) M2 credit a second mark if all four parts of the required structures and 1 names are correct. (credit linear structures) (insist on the alkyl groups being attached clearly by - bonds) (b) (i) Ml curly arrow from middle of = bond to atom on -Br 1 (penalise M1 if partial negative charge or formal positive charge on ) (penalise Ml if pent-2-ene is used) M2 curly arrow from -Br bond to side of Br atom 1 M correct structure for correct secondary carbocation 1 M4 curly arrow from lone pair on bromide ion to the positive carbon of 1 carbocation, ensuring that bromide ion has a negative charge. (with the exception of pent-2-ene, if the wrong alkene is used, only penalise the structure M) (penalise the use of two dots in addition to a covalent bond, once only) Mill ill igh School 2

3 8. (ii) 1-bromopentane 1 (iii) Ml 2-bromopentane is formed via the secondary (or 2 ) carbocation 1 OR 1-bromopentane is formed via the primary (or 1 ) carbocation M2 a secondary carbocation is more stable than a primary carbocation - 1 award this mark only if the quality of language justifies the award. (the argument must involve clear statements about carbocations) M4 arrow :Br [9] (i) arrow Br M1 arrow M2 If wrong carbocation, lose structure mark If wrong alkene, lose structure mark an still score ¾ i.e. penalise M Penalise M2 if M carbocation polarity included incorrectly no bond between and Br bond is shown as or (ii) 2 2 credit secondary carbocation here if primary carbocation has been used in (i) : Ignore attack on this carbocation by Br 9. (a) melting point increases boiling point increases or they are liquids, the higher members are solids density increases viscosity increases max 2 (b) addition polymerisation 2 (c) (i) O 2 5 O - must show the functional group 1 (ii) vapour phase / high temperature (00 ± 50 ) high pressure 70cl ± 20 if high T and high p, then only 1 mark, value for either gives 2nd mark strong acidic catalyst / PO 4 (iii) electrophilic addition 2 5 [5] [10] Mill ill igh School

4 10. (i) Isomer 1 Isomer 2 either order [credit and ] (ii) restricted rotation OR no rotation OR cannot rotate [] 11. (a) electrophilic addition : 5 Mill ill igh School 4

5 (b) or 1 (c) ester or alkoxy alcohol 1 (d) (i) O 2 2 O (ii) high electron density of double bond repels O or nucleophile [10] 12. (a) geometrical or cis-trans isomers due to restricted rotation 2 (b) (i) Br 2 2 Br (ii) electrophilic addition (iii) both secondary but one is more stable 6 [8] 1. (i) the same general formula or n 2n / the same functional group / a = / a double bond / differ from their immediate neighbour by 2 1 (ii) allow all straight chain alkenes increases not just pent-l-ene highest ; allow ethene lowest, pent-l-ene highest 1 Mill ill igh School 5

6 (iii) methylpropene / 2 methylpropene not 2-methylprop-2-ene ignore wrong punctuation or allow 1 mark for but-2-ene with its correct structure 2 minimum structure is = or = ( ) atalyst (c) phosphoric acid or (c) sulphuric acid Not dilute accept correct formula onditions Temp = igh or Temp = medium or moderate or [4] Pressure = igh or 5 20 Mpa or atoms Pressure = igh or 2 4 Mpa or atoms If. wrong, no catalyst given, allow phosphoric acid conditions Equation 2 = 2 2 O 2 O allow 2 4 allow 2 5 O not [4] 15. M1 X is 1,2-dibromoethane only 1 M2 electrophilic addition 1 (both words needed) M the double bond is a centre of electron density 1 OR electron-rich OR nucleophilic OR a source of an electron pair OR a pi cloud/bond of electrons M4 a dipole or polarity is induced/created/formed in the Br-Br bond/molecule - 1 award this mark only if the quality of language justifies the award. [15] Mill ill igh School 6

7 16. An appropriate alkene; 2 2 or ( ) Isomer 1 1 Isomer 2 1 Position isomerism 1 Mechanism electrophilic attack and electron shift to Br (Unless used) 1 carbocation 1 reaction with carbocation 1 [Allow mechanism marks for the alkene ] [Allow one mark if mechanism for minor product given] 17. (a) Reaction 1 2 O or steam [7] (b) 4 M4 2 2 structure M1 Br :Br M2 M Penalise M2 incorrect δ / δ Penalise δ on alkene (M1) Penalise dots on bonds once Penalise M4 (structure) for use of wrong alkene Penalise M1 for use of Br 2 [5] 18. ethane tetrahedral (or d shown in diagram) 109( 1 2 ) ethene (trigonal) planar 120 bond lengths: in ethane longest or } = in ethene shortest } in ethene : 2 pairs of e/greater electron density /π bond (a) Br ( ) ( ) ( ) [6] :Br Br 2 bromo 2 methylpentane tertiary carbonium ion more stable than secondary 7 Mill ill igh School 7

8 20. (b) geometrical or cis trans isomerisation hex ene or hex 2 ene R R R 2 R (cis) (trans) 4 Br :Br Br 2 = electrophilic addn tertiary 2-bromo-2-methylpentane or 2 2 Br secondary -bromo-2-methylpentane [11] tertiary more stable than secondary [1] 21. (a) A alkene B halogenoalkane / bromoalkane / alkyl halide / haloalkane alcohol (ignore primary, secondary) (b) (i) addition ignore nucleophilic / electrophilic / free radical 1 (ii) substitution not replacement / displacement 1 (c) Sodium hydroxide / NaO / KO not just hydroxide (B to ) aqueous not dilute (B to A) alcoholic mark alternatives as (d) ignore references to concentration and temperature (d) (i) ( )Br NaO = 2 NaBr 2 O (ii) ( )Br NaO ( )O NaBr allow molecular formulae 7 Br; 8 O; 6 allow ionic versions (with O, Br ) 2 (e) arrow from O of O to joined to Br lone pair not needed Br polarity shown by δ δ or heterolytic fission of Br bond shown by arrow from bond between and Br to Br or intermediate with partial bonds and minus sign Br as product allow all marks if 1-bromopropane identified as B Mill ill igh School 8 [1]